The northwest of Iberia experiences important tectonic activity that has led to several episodes of seismic swarms. Despite substantial knowledge of the surface structures that could be responsible for this activity, their distribution at depth remains unclear. Geophysical research and rheological data display important discrepancies concerning the deep structure of the area. In order to shed light on the processes that control deep seismicity and their relationship with surface structures, we combine the analysis of seismic activity in northwest Iberia with the interpretation of sandbox experiments simulating tectonic structures similar to those observed. The structural interpretation of the modeling results was conducted by analyzing the surface particle image velocimetry field. Additionally, yield strength and brittle‐ductile transition zone (BDTZ) maps were constructed from model sections. The modeling results show a direct relationship between the main active structures developed along pre‐existing weak zones and the observed variations in crustal thickness. Moreover, these thickened zones correspond to the sectors where the BDTZ in the crust deepens. Therefore, the anomalous thickness and lateral variations of the seismogenic zone cannot be solely explained by rheological or structural changes but result from a combination of factors such as fluid pressure and the location of fractures at depth, which controls the fluid migration responsible for the failure of crustal faults. These factors can trigger seismic activity at depth and may control the observed thickness variations in the BDTZ.

中文翻译：

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西北部伊比利亚脆性-韧性过渡带横向强度变化和深度的新见解

伊比利亚西北部经历了重要的构造活动，这导致了数次地震群发。尽管对可能导致此活动的表面结构有大量了解，但它们在深度上的分布仍不清楚。地球物理研究和流变数据显示出有关该地区深层结构的重要差异。为了阐明控制深地震活动及其与表层结构的关系的过程，我们将对伊比利亚西北部地震活动的分析与模拟类似于构造构造的沙箱实验的解释相结合。通过分析表面粒子图像测速场对建模结果进行结构解释。此外，屈服强度和脆性-延性转变区（BDTZ）图是从模型部分构建的。模拟结果表明，沿先前存在的薄弱区域发展的主要活动结构与观测到的地壳厚度变化之间存在直接关系。此外，这些增厚的区域对应于地壳中BDTZ加深的区域。因此，不能单独用流变或结构变化来解释地震发生带的异常厚度和横向变化，而是由诸如流体压力和深部裂缝位置等多种因素共同导致的，这种因素控制着导致流体破裂的流体运移。地壳断层。这些因素可以触发深处的地震活动，并可以控制BDTZ中观察到的厚度变化。